FBI investigators are believed to have sifted through a massive 650,000 emails in just nine days to determine whether Mrs Clinton had a case to answer.

The emails were discovered on a device owned by disgraced former congressman Anthony Weiner, who is under investigation for allegedly sending explicit messages and graphic pictures to a 15-year-old girl.

Congressman Weiner was married to Mrs Clinton’s top aide, Huma Adebin, though the pair are now divorced.

In a letter sent to Congress on October 28, Mr Comey dropped the bombshell that he was set to re-start the FBI probe into the server after the discovery of the “pertinent” exchanges, to see if any contained classified information.